The chart below shows long and short positions in the peso over the past year, via the CFTC's weekly Commitment of Traders report.

Long positions have been surging recently while short positions have stagnated. And as the green line at the bottom shows, the net position on the peso just went positive – i.e., there are now more longs than shorts:

And the peso has been strengthening in tandem with the build in long positions. This chart shows the dollar weakening against the pso.

When asked what his single best buy in the foreign exchange market right now was, Nordvig said, "Euro-Mex is a play that we like," and that the peso is "one of the most attractively valued" currencies. In other words, Nordvig likes a trade selling the euro and buying the peso.

Why? It's pretty simple. Nordvig said, "For example, if you look at growth – growth has been declining all over the world. The only country that is holding up? Mexico."

But Nordvig isn't the only one loving the peso trade right now.

Another big proponent is Jim O'Neill, the chairman of Goldman Sachs Asset Management and the emerging markets guru who coined the term "BRIC."

In his latest Viewpoints letter, O'Neill recommended a long-peso, short-Australian dollar trade. Buying the Australian dollar is a good way to bet on China growth, and O'Neill sees a lot of people turning bearish on this theme.

Once again, the best currency to buy with the currency you want to get rid of, according to Jim O'Neill, is the peso.

Gluskin-Sheff economist David Rosenberg explained that Mexico is the one country that seems to be decoupling from the global slowdown:

If there is a country out there that does appear to have "decoupled" and we have discussed this before, it is Mexico, where industrial production managed to turn in a hefty 1.3% gain in June, the best performance since September of last year and higher than market expectations. Fiesta yes; siesta no.

Mexican industrial production has been roaring since recovering from the global downturn of 2008 and 2009. The pace of expansion slowed a bit in 2012, but it's turning back up again:

The chart at the top showing the build in long positions may suggest the trade is getting crowded. On the other hand, there are plenty who remain short.